1. Field of the Invention
The invention relates to a gas spring of the push type that has a pressure medium-filled pressure tube, which has a pressure tube connector element for the external attachment of the push-type gas spring; and a piston, which is operable to slide back and forth axially in the pressure tube and has a piston rod, wherein the piston rod extends out of the pressure tube from a first end surface of the pressure tube and has a piston rod connector element for the external attachment of the push-type gas spring.
2. Description of the Related Art
A push-type gas spring of this type is generally known as a means for lifting heavy objects such as the rear hatches or engine-compartment hoods of motor vehicles, etc. The push-type gas spring is a hydropneumatic adjusting element with a pressure tube, a piston with a piston rod, and connectors for attaching the push-type gas spring at one end to, for example, the chassis of a motor vehicle and at the other end to a rear hatch of the motor vehicle. A pushing force in an outward-travel direction of the pressurized gas spring is produced by the presence of a compressed pressure fluid in the pressure tube; this fluid acts with the same pressure on cross-sectional areas of the piston of different sizes.
So that a pulling force can be exerted on the connectors, pull-type gas springs are in common use. There are two different known designs for pull-type gas springs. One variant uses a piston sealed in a tube, whereas the other variant uses two piston rods of different diameter. Both variants suffer from the disadvantage of high internal friction and short life-span.
An oil-actuated cylinder with a piston rod in the form of a push-type or pull-type gas spring for limiting a drive force in a crank drive is also known. The cylinder has a complicated design, because it must be connected by an external oil connector and a pressure switching valve to a fluid reservoir and a pump, which produces the preloading pressure. A continuous process of external pressure and volume compensation takes place in the cylinder.